.TH std::begin,std::cbegin 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::begin,std::cbegin \- std::begin,std::cbegin

.SH Synopsis
   Defined in header <array>
   Defined in header <deque>
   Defined in header <flat_map>
   Defined in header <flat_set>
   Defined in header <forward_list>
   Defined in header <iterator>
   Defined in header <list>
   Defined in header <map>
   Defined in header <regex>
   Defined in header <set>
   Defined in header <span>
   Defined in header <string>
   Defined in header <string_view>
   Defined in header <unordered_map>
   Defined in header <unordered_set>
   Defined in header <vector>
                                                                (since
   template< class C >                                          C++11)
   auto begin( C& c ) -> decltype(c.begin());                   (until
                                                                C++17)
   template< class C >                                          (since
   constexpr auto begin( C& c ) -> decltype(c.begin());         C++17)
                                                                        (since
   template< class C >                                                  C++11)
   auto begin( const C& c ) -> decltype(c.begin());                     (until
                                                                        C++17)
   template< class C >                                                  (since
   constexpr auto begin( const C& c ) ->                                C++17)
   decltype(c.begin());                                 \fB(1)\fP
                                                                                (since
   template< class T, std::size_t N >                                           C++11)
   T* begin( T (&array)[N] );                               \fB(2)\fP                 (until
                                                                                C++14)
   template< class T, std::size_t N >                                           (since
   constexpr T* begin( T (&array)[N] ) noexcept;                \fB(3)\fP             C++14)
   template< class C >

   constexpr auto cbegin( const C& c ) noexcept(/* see                  \fB(4)\fP     (since
   below */)                                                                    C++14)

       -> decltype(std::begin(c));

   Returns an iterator to the beginning of the given range.

   1,2) Returns c.begin(), which is typically an iterator to the beginning of the
   sequence represented by c.
   1) If C is a standard Container, returns a C::iterator object.
   2) If C is a standard Container, returns a C::const_iterator object.
   3) Returns a pointer to the beginning of array.
   4) Returns std::begin(c), with c always treated as const-qualified.
   If C is a standard Container, returns a C::const_iterator object.

   range-begin-end.svg

.SH Parameters

   c     - a container or view with a begin member function
   array - an array of arbitrary type

.SH Return value

   1,2) c.begin()
   3) array
   4) c.begin()

.SH Exceptions

   4)
   noexcept specification:
   noexcept(noexcept(std::begin(c)))

   Overloads

   Custom overloads of begin may be provided for classes and enumerations that do not
   expose a suitable begin() member function, yet can be iterated. The following
   overloads are already provided by the standard library:

   std::begin(std::initializer_list)                    overloads std::begin
   \fI(C++11)\fP                                              \fI(function template)\fP
   std::begin(std::valarray)                            overloads std::begin
   \fI(C++11)\fP                                              \fI(function template)\fP
   begin(std::filesystem::directory_iterator)           range-based for loop support
   end(std::filesystem::directory_iterator)             \fI(function)\fP
   \fI(C++17)\fP
   begin(std::filesystem::recursive_directory_iterator) range-based for loop support
   end(std::filesystem::recursive_directory_iterator)   \fI(function)\fP

   Similar to the use of swap (described in Swappable), typical use of the begin
   function in generic context is an equivalent of using std::begin; begin(arg);, which
   allows both the ADL-selected overloads for user-defined types and the standard
   library function templates to appear in the same overload set.

 template<typename Container, typename Function>
 void for_each(Container&& cont, Function f)
 {
     using std::begin;
     auto it = begin(cont);
     using std::end;
     auto end_it = end(cont);
     while (it != end_it)
     {
         f(*it);
         ++it;
     }
 }

   Overloads of begin found by argument-dependent lookup can be used to
   customize the behavior of std::ranges::begin, std::ranges::cbegin, and \fI(since C++20)\fP
   other customization pointer objects depending on std::ranges::begin.

.SH Notes

   The non-array overloads exactly reflect the behavior of C::begin. Their effects may
   be surprising if the member function does not have a reasonable implementation.

   std::cbegin is introduced for unification of member and non-member range accesses.
   See also LWG issue 2128.

   If C is a shallow-const view, std::cbegin may return a mutable iterator. Such
   behavior is unexpected for some users. See also P2276 and P2278.

.SH Example


// Run this code

 #include <iostream>
 #include <iterator>
 #include <vector>

 int main()
 {
     std::vector<int> v = {3, 1, 4};
     auto vi = std::begin(v);
     std::cout << std::showpos << *vi << '\\n';

     int a[] = {-5, 10, 15};
     auto ai = std::begin(a);
     std::cout << *ai << '\\n';
 }

.SH Output:

 +3
 -5

.SH See also

   end
   cend           returns an iterator to the end of a container or array
   \fI(C++11)\fP        \fI(function template)\fP
   \fI(C++14)\fP
   ranges::begin  returns an iterator to the beginning of a range
   (C++20)        (customization point object)
   ranges::cbegin returns an iterator to the beginning of a read-only range
   (C++20)        (customization point object)

.SH Category:
     * conditionally noexcept
